Fatigue Performance of Flax/PLA Composites Enhanced by TPU Layer: Characterization and Optimization

This study investigates the fatigue behavior of 3D-printed, fully bio-based flax/PLA composites enhanced with viscoelastic thermoplastic polyurethane (TPU) interlayers, contrasting them with unreinforced counterparts. Leveraging additive manufacturing, composites with tailored stacking sequences and TPU layer thicknesses are subjected to quasi-static bending, progressive fatigue-to-failure, and cyclic loading tests across multiple stress levels and temperatures (20–50[Formula: see text]C). Results reveal that TPU integration improves energy dissipation (60% hysteresis area increase) and damping capacity while mitigating stiffness loss — a critical trade-off in viscoelastic composites. Temperature-dependent analyses demonstrate retained fatigue resistance at 50[Formula: see text]C, with optimized TPU configurations reducing stiffness degradation by 25% compared to non-reinforced systems. By correlating layer architecture (thickness, placement) with dynamic properties such as stiffness evolution and crack propagation resistance, this work establishes a framework for tunable bio-composite design. These findings highlight the viability of 3D-printed TPU/PLA/flax laminates in applications demanding sustainability, durability, and adaptive thermomechanical performance, such as automotive components and renewable energy systems.